1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly to a handle attachment for an electrical switching apparatus, such as a circuit breaker. The invention also relates to an assist mechanism for handle attachments and to electrical switching apparatus having handle attachments with assist mechanisms.
2. Background Information
Circuit breakers are generally old and well known in the art. Examples of circuit breakers are disclosed in U.S. Pat. Nos. 5,341,191 and 5,471,184. Circuit breakers are used to protect electrical circuitry from damage due to a trip condition, such as, for example, an overcurrent condition, an overload condition, an undervoltage condition, or a relatively high level short circuit or fault condition. Molded case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by way of a handle disposed on the outside of the case, or automatically by way of a trip unit, in response to a trip condition.
Separately attachable handles for circuit breakers are also known. These include a variety of handle attachments, such as rotating handles which often serve secondary functions and include auxiliary features. For example, in addition to providing an operating handle, the handle attachment may also serve as a status indicator (e.g., trip indicator), and it may include a handle locking device. See, e.g., U.S. Pat. No. 6,194,983.
When the handle attachment is attached directly to the face of the molded case circuit breaker, such a configuration is commonly referred to as “closely-coupled.” However, not all handle attachments are closely-coupled. Conversely, some are coupled to the circuit breaker by way of an intermediate linkage or actuating assembly. See, e.g., U.S. Pat. No. 6,504,460. For example, circuit breakers are often recessed within a switchgear cabinet or other enclosure. In such instances, the handle attachment may be disposed, for example, on the door of the switchgear cabinet, with the linkage or actuating assembly interconnecting the handle attachment to the operating member of the circuit breaker in order that it may be actuated and, in the instance of a status indicator, a status indication may be seen, from the exterior of the switchgear cabinet.
FIGS. 1 and 2 show a closely-coupled handle attachment 2 as employed on a molded case circuit breaker 4. The handle attachment 2 includes an insulating case 6 which may be coupled to the housing 8 of the circuit breaker 4 by any suitable fastening mechanism, such as the exemplary screws 10, shown in FIG. 1. In the example of FIG. 1, the attachment 2 has a pivoting handle 12 which is operable between three positions, an ON position, an OFF position, and the intermediate tripped position, as shown. Thus, the handle attachment 2 also functions as a status or trip indicator for the circuit breaker 4.
The interior of the handle attachment 2 is shown in FIG. 2. Generally, the handle attachment 2 includes the exterior handle 12 and the actuating assembly 14 for interconnecting and translating energy from the operating member 16 (e.g., handle) of the circuit breaker 4 (shown in phantom line drawing in FIG. 2) to the handle 12 of the attachment 2. The operating member 16 protrudes from an opening (indicated generally by reference 9 in FIG. 2) in the circuit breaker housing 8. In the example of FIG. 2, the actuating assembly 14 comprises a rack 18 with an opening 20 for engaging the circuit breaker operating handle 16, a main gear 22, and a pinion 24 for translating pivotal movement of the circuit breaker operating handle 16 and the associated linear movement of the rack 18, into rotation of the main gear 22 which in turn pivots handle 12 which is coupled thereto. However, any known or suitable mechanism for translating movement of the circuit breaker operating handle 16 into movement of the attachment handle 12 could be employed. The actuating assembly 14 further includes a gear retainer 26 for securing the main gear 22 and pinion 24 in place, and a rack guide 28 which interacts with and moveably supports the rack 18 between the gear retainer 26 and the rack guide 28. The foregoing assembly is described in further detail in U.S. Pat. No. 6,194,983, which is incorporated herein by reference.
In addition to the closely-coupled configuration shown in FIG. 1, the handle attachment 2 can be employed in a variety of non-closely-coupled configurations (not shown), as previously discussed, and in applications such as the example shown in FIG. 2, wherein the attachment 2 is adapted to interact with, for example, the door (not shown) of a switchgear cabinet (not shown). A biasing element, such as the torsion spring 32, is also included in order to facilitate the door interlock member 30 to interact (e.g., interlock) with the cabinet door (not shown).
However, known handle attachments, including those previously described, suffer from a number of disadvantages. Among them is the fact that for relatively small circuit breakers (e.g., without limitation, about 120 to about 150 A, or less), the mechanical advantage (e.g., lever force) provided by the relatively small circuit breaker operating member 16 is often insufficient to move the components (e.g., actuating assembly 14), of the handle attachment 2 and, in particular, the handle 12 thereof. While this is true of all handle attachments (e.g., handle attachment 2 of FIGS. 1 and 2), it is particularly true with respect to handle attachments which are not of the closely-coupled variety (not shown) in which case comparatively significant force is required to translate the energy generated by the moving circuit breaker operating member 16 to the handle 12 of the handle attachment 2. More specifically, the linkage between the operating member 16 and handle 12 can span a distance of as much as about 18 inches (45.72 centimeters), or more. Therefore, the insufficient mechanical force produced by the relatively small operating member 16 of the circuit breaker 4 can potentially fail to move the actuating assembly 14 and thus the handle 12, resulting in an incorrect status indication as shown by the handle 12 on the handle attachment 2. For example, without limitation, for a three-position circuit breaker of the type shown in FIGS. 1 and 2, wherein the tripped handle position is between the ON and OFF positions, movement of the relatively small circuit breaker operating member 16 might not be capable of generating enough leveraging energy to move the handle 12 of the attached handle attachment 2 sufficiently enough to indicate the occurrence of a trip condition.
Additionally, handle assist mechanisms (e.g., without limitation, a torsional spring (not shown); a coil spring (not shown)) that might be contemplated in order to address the foregoing problem, would fail to provide the variation in force required for each of the different operating member 16 positions. For instance, torsion springs and coil (e.g., tension; compression) springs provide an increasing compression force the further they are extended. Therefore, use of such a spring as a handle assist mechanism could result in the operating member 16 being excessively biased, for example, from the ON position or the tripped position toward the OFF position. In other words, a slight bump or other disruption of the circuit breaker 4 or handle attachment 2 could, for example, result in the circuit breaker 4 being undesirably, unintentionally turned OFF. This problem could also occur with relatively small circuit breakers having other operating member configurations (e.g., two-position operating members).
There is, therefore, room for improvement in assist mechanisms for handle attachments, in handle attachments for electrical switching apparatus and in electrical switching apparatus having handle attachments.